The present invention relates to an electron beam exposure method for performing exposure while a sample table is being moved continuously and an apparatus and a device using the same, and particularly to an electron beam exposure method and apparatus capable of preventing degradation in the accuracy of exposure due to glitch noise of a DA converter and reducing the number of trace region pass-changeovers, and a device manufactured using the same.
As one of methods for implementing high throughput of an electron beam exposure apparatus may be mentioned continuous shifting exposure for performing exposure while a sample table is being moved continuously. Trace control for first detecting the amount of movement of the sample table and next feeding back the amount of movement thereof for the purposes of the deflection of an electron beam in real time is essential to perform the continuous shifting exposure. For example, Continuous writing method for high is speed electron-beam direct writing system HL-800D (J.Vac.Sic.Technol.B11(6)) is disclosed as an example of the trace control, which has been known to date.
FIG. 3 is a diagram for describing the trace control method employed in the above-described conventional example.
The operation of FIG. 3 will be explained. Exposure is effected on a sample 11 placed on a sample table 12 by means of an electron beam 10 while the sample table 12 is being moved continuously. First, a laser interferometer 2 measures the coordinates of the sample table 12 with the exposure sample 11 placed thereon. A trace signal calculation unit 6 calculates the amount of deflection equivalent to displacements of the coordinates of the sample table 12 and coordinates to apply the electron beam, i.e. trace deflection data. A pattern generator 1 is capable of generating various device""s pattern data inclusive of the sample 11. Exposure deflection data outputted from the pattern generator 1 and trace deflection data outputted from the trace signal calculation unit 6 are respectively converted to analog values by DA converters 7 and 8. These two analog values are added together by an analog adder 9, followed by input to a deflector 5. Thus, the deflector 5 deflects the electron beam 10 to a desired position on the exposure sample 11.
A cycle for updating trace deflection data calculated by the trace signal calculation unit 6 is determined from the transfer speed of the sample table 12 and required exposure accuracy. Namely, the updating cycle becomes short as the transfer speed of the sample table 12 becomes fast and the exposure accuracy becomes high. In the conventional example, the trace signal or trace deflection data is updated in a cycle of 100ns (10MHz). Since the DA converter 7 used for exposure deflection and the DA converter 8 used for trace deflection are different in required property, DA converters 7 and 8 dedicated to them are provided. Namely, the DA converter 7 used for exposure deflection is activated in synchronism with applying (shot) timing of the electron beam and the electron beam is applied after the output thereof has been settled. Thus, since the settling time of the DA converter 7 results in exposure wasting time, its responsivity must be made fast. On the other hand, the DA converter 8 used for trace deflection needs to update data in a cycle shorter than the DA converter 7, i.e., during the application of the electron beam. Therefore, DA converters small in glitch noise produced upon changes in the outputs of the DA converters are used.
When the amount of deflection based on the trace deflection exceeds a predetermined value, a trace region pass-changeover operation for adding the amount of the trace deflection to the amount of deflection of a high-level deflector 23 and restoring the amount of the trace deflection to the initial value is performed. Namely, when the amount of the deflection exceeds the predetermined value since the high-level deflector 23 shown in FIG. 3 has a deflection range larger than that of the low-level deflector 5, the trace deflection data is transferred from the trace signal calculation unit 6 to a DA converter 22 for the deflector 23 through the pattern generator 1, and the value calculated by the trace signal calculation unit 6 is returned to 0.
Since the amount of movement of the sample table 12 can be fed back for the deflection of the electron beam 10 in real time according to the above-described exposure method, exposure can be implemented at high speed and with high accuracy while the sample table 12 is being moved continuously.
As described above, the DA converter is used for the deflection of the electron beam in the electron beam exposure apparatus. The DA converter is commonly comprised of a plurality of current sources different in weight. There are provided switches for turning on and off the respective current sources. Necessary values are selected from the plurality of current sources and the selected outputs are added together and thereafter outputted, whereby an arbitrary large output can be obtained. Since, however, the respective switches vary in operating time, a current having an unintentional magnitude might be outputted when data is switched over to another. This is called xe2x80x9cglitch noisexe2x80x9d. The magnitude of the glitch noise is determined depending on the number of the activated switches and the sizes of the current sources switched thereby. Thus, the maximum glitch noise is produced in the case of a {fraction (1/2+L )} full scale at which all the bits of input data are inverted. If a full scale 15 is represented in 4 bits based on a binary number (four switches), for example, then the maximum value results in xe2x80x981111xe2x80x99 (15 represented in a decimal number) and the minimum value results in xe2x80x980000xe2x80x99 (0 similarly). Since the {fraction (1/2+L )} full scale is set between 7 and 8, all the bits are interchanged at the time of a changeover from xe2x80x980111xe2x80x99 to xe2x80x981000xe2x80x99, so that switching timings of all the switches are mismatched with one another, thus leading to the generation of the maximum glitch noise.
Since the generation of the glitch noise is a problem about the structure of each DA converter in this way, it is very difficult to reduce the glitch noise. Although the glitch noise can be reduced by inserting a filter, a delay in response is produced so that it could not lead to practical applications.
The deflection of the electron beam by the electron beam exposure apparatus of the sample table continuous shifting system can be roughly divided into exposure deflection for exposure and trace deflection for trace control. As to the exposure deflection, deflection data is set to a DA converter and a beam is kept in an off state until the output thereof is settled. Thus, the glitch noise produced upon transition of the output does not influence the result of exposure. On the other hand, the trace deflection for feeding back the amount of movement of a sample table is deflection for correcting the amount of movement of the continuously-moved sample table according to the deflection of the electron beam. Therefore, the glitch noise is produced in the DA converter 8 in FIG. 3. The execution of high-accuracy trace deflection needs to update trace deflection data in a short cycle. It is thus necessary to update the trace deflection data in a cycle shorter than that for graphics exposure, and the data is updated even during the application of the electron beam. When the trace deflection data is brought to data which causes large glitch noise in the DA converter, a displacement in exposure position due to the influence of the glitch noise occurs, so that the accuracy of exposure is degraded. Thus, it is necessary to limit the range of trace deflection so that the DA converter is used within a range represented in such a level that the glitch noise does not influence exposure.
However, a problem arises in that when the range of the trace deflection becomes narrow, the number of trace region pass-changeovers increases and a reduction in exposure speed occurs due to wasting time produced at this time.
Therefore, an object of the present invention is to provide an electron beam exposure method and apparatus capable of solving these conventional problems and preventing degradation in the accuracy of exposure due to glitch noise of a DA converter used for trace deflection to thereby carry out high-accuracy exposure, and increasing a tracing range to thereby reduce the number of trace region pass-changeovers and provide high-speed exposure.
In order to achieve the above object, there is provided an electron beam exposure apparatus according to the present invention, comprising means for determining displacements of a position of a sample table and a position to apply an electron beam, a first trace deflection correcting unit for determining a first amount of trace deflection for correcting the determined displacements in synchronism with timing provided to apply the electron beam, a second trace deflection correcting unit for setting the amount of correction by the first trace deflection correcting unit as the point of origin and determining a second amount of trace deflection for correcting the amount of a variation from the point of origin in a cycle shorter than a correcting cycle for the first trace deflection correcting unit, and wherein the first amount of trace deflection and the second amount of trace deflection are added to the amount of deflection of an electron beam for graphics exposure and the result of addition is outputted, whereby the displacements of the position of the sample table and the position to apply the electron beam are corrected.
There is also provided an electron beam exposure method according to the present invention, comprising the following steps of calculating displacements of a position of a moved sample table and a position to apply an electron beam, sampling the calculated displacements in synchronism with timing provided to apply the electron beam, calculating a first amount of trace deflection for correcting the sampled displacement according to the deflection of the electron beam, setting the first amount of trace deflection as the point of origin and calculating a second amount of trace deflection for correcting the amount of a variation therefrom in a cycle shorter than a calculation cycle for the first amount of trace deflection, adding the first amount of trace deflection and the second amount of trace deflection to the amount of exposure deflection data calculated by a pattern generator, and driving a deflector according to the added amount of deflection data.
Thus, the value or amount corrected by the second trace deflection correcting unit activated in the short cycle during the application of the electron beam can be limited to a slight value, and the glitch noise can be prevented from occurring. Further, the addition of an offset to the first amount of trace deflection and the second amount of trace deflection allows avoidance of bit patterns large in glitch, and the number of trace region pass-changeovers can be reduced by increasing a tracing range.